1. Field of the Invention
The invention relates to flushing gas pockets from a manifold. In one aspect, the invention relates to flushing gas pockets from a manifold that forms a part of a liquid sampling system while in another aspect, the invention relates to flushing gas pockets from a multi-port valve manifold disposed within a liquid sampling system that includes a sensor for monitoring the health of a slurry used in a chemical-mechanical polishing system, the sensor sensitive to gas pockets.
2. Description of the Related Art
A chemical-mechanical polishing (CMP) system is often employed in the microelectronics industry to contour and/or polish semiconductor wafers. These systems typically contain and employ a “slurry” which is cycled throughout the system such that the slurry contacts and/or impinges upon the wafers. As the cycling slurry impacts and/or passes over the wafers, the wafers are contoured and polished.
In order to maintain the consistency, performance, efficiency, and/or usefulness of the system, the “health” of the slurry must be maintained. Slurry instability, external contamination, or process conditions (e.g., shear-inducing pressure gradients, flow rates, and exposure to air) may all compromise slurry health. Thus, slurry properties (e.g., specific gravity, pH, weight percent solids, ionic contamination level, zeta potential, and particle size distribution (PSD)), are often closely monitored by sampling systems.
Of all the slurry health properties, perhaps the most important and frequently monitored is PSD. In the industry, PSD can be observed using a variety of instruments such as sensors, analyzers, and like devices (collectively referred to as sensors) that are commercially available from a host of manufacturers. For example, one such sensor is the AccuSizer 780/OL (AccuSizer) manufactured by Particle Sizing Systems (PSS) of Santa Barbara, Calif.
Unfortunately, while these PSD sensors are generally suitable for analyzing slurry, these sensors can possess disadvantages in some circumstances. Certain of these sensors are generally limited to sampling a single slurry at a single sampling point (i.e., a location within a CMP system from where a sample is taken). In other words, each CMP system, as well as each slurry used within that CMP system, would require a dedicated sensor. Since integrated circuit manufacturers, as well as others, often desire to analyze numerous different slurries, from multiple sampling points (i.e., locations), a one-to-one ratio of sensor to slurry would dramatically increases costs. Therefore, a liquid sampling system, using a single sensor, capable of monitoring one of a plurality of slurries from multiple sampling points was developed.
The liquid sampling system was built around a sensor to permit measurement of a number of different slurries, from multiple sample points, by utilizing a multi-port valve manifold. The multi-port valve manifold is operable, within the liquid sampling system, to selectively route any one of a number of different slurries, from a variety of locations, to a single sensor for PSD analysis.
While developing and testing the liquid sampling system, the need to sufficiently flush and/or rinse the multi-port valve manifold substantially free of gas pockets (i.e., bubbles) was revealed. The gas pockets, e.g., air, nitrogen, etc., are typically entrained in a liquid that is disposed within the manifold and/or clinging to surfaces (e.g., walls) of the manifold and associated components, hiding inside crevasses in the manifold, and otherwise trapped inside the manifold. If the gas pockets are permitted to pass through and/or proximate the sensor, the gas pockets can interfere with the operation and accuracy of the sensor. Moreover, since the gas pocket can contain, trap, hold, and/or support contaminants (e.g., debris, impurities, etc.), the contaminants can also interfere with the operation and accuracy of the sensor. As a result, if either or both of the gas pockets and the contaminants are permitted to pass through and/or proximate the sensor, the sensor and the liquid sampling system can return PSD results, data, and/or output that is skewed, unreliable and/or inaccurate.
Effectively removing gas pockets from a manifold is difficult, especially at relatively low pressures. Gas pockets have a tendency to cling to the surfaces (e.g., interior walls) of the manifold and associated components. Likewise, gas pockets often form in crevasses and other areas within the manifold that are difficult to access with flush or rinse liquids. Thus, a method of effectively flushing a manifold of residual gas pockets within a liquid sampling system is desirable.